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Building a Doodle Bot Kit 


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Building a Doodle Bot Kit 

Written By: OddBot 


Screwdriver, small. Phillips (1) 
This tool is supplied in the kit 


USB cable. standard-A to mini-B (1) 


The Doodle Bot is a simple robot kit for beginners that can draw pictures and write text 
messages with a pen. 

Sample code allows the robot to write messages created by the user. The size of the writing 
can be changed. 

The Robot is programmed using the Arduino IDE and a USB cable. 4x AAA batteries are 

© Make Projects 

Page 1 of 18 

Building a Doodle Bot Kit 

Step 1 — Familiarize yourself with the kit before you start 

• Before you begin assembly, check 
that you have all the parts. 

• In the part list, each part has a 
number. For example, the rubber 
tire is part #3. These numbers are 
used in the instructions to identify 
the parts. 

• The instruction manual 
includes printed rulers. Use 
these to check the length of your 

• You can download the manual from 

Step 2 — Make your wheels 

7e the ruler to check tl 
length of your screws 

fOfilrn IPmin 3(Jfim 

• Start by removing the protective 
film from the laser cut wheel pieces 
(part #2). 

• Gently stretch the rubber tires (part 
#3) over the wheels. 

© Make Projects 

Page 2 of 18 

Building a Doodle Bot Kit 

Step 3 — Identify the motors and the servo 

Center your settfO and fit the 
servo horn so it is pointing 
Straight down, 

• This robot uses two geared motors 
(part #5) that were servos but have 
had their control circuit removed. 
These motors only have two wires. 

• One servo (part #6) is used at the 
front of the robot to raise and lower 
the pen. This servo has 3 wires. 

Step 4 — Fit mounting brackets to your motors 


Use the ruler to checl 
length of your screws 

2Dmm 30rtim 40mr. 



• Use the printed ruler to identify your M2x5 screws (part #11). 

• Partially insert six M2x5 screws into the 90° angle brackets (part #9). 

• Insert your mounting brackets into the motor mounting slots and gently tighten the screws 
until the bracket is held firmly. 

• Pay careful attention to the way the brackets are mounted as you have a left and 
right motor. The servo can only mount on the left side. 


© Make Projects 

Page 3 of 18 

Building a Doodle Bot Kit 

Step 5 — Prepare the base and sensors 


• Before we can build upon the base plate (part #1) we need to remove the protective film. 

• Our robot uses two small magnetic sensors (Hall-effect sensors - part #21) that switch on 
or off in response to a magnetic field. Bend their leads at roughly 90° , close to the sensor 
so they can hang over the edge of the base plate. 

© Make Projects 

Page 4 of 18 

Building a Doodle Bot Kit 

Step 6 — Mount your motors and sensors on the base plate 

• The easiest way to mount the left and right motors is to start with a single M2x8mm screw 
(part #14) passing through a fiberglass strip (part #25), through the base plate (part #1) 
and into the motor mounting bracket (part #9) on the other side. Do not tighten the screw 

• While the screw is loose, slide your sensor under the strip as shown and then add your 
second M2x8mm screw. Align the sensor so it sits directly above the output shaft of the 
motor and gently tighten the mounting screws until the fiberglass strip bends slightly. 
Repeat these steps for the other motor. 

• Now mount the servo (part #6) using the last two M2x5mm screws. 

© Make Projects 

Page 5 of 18 

Building a Doodle Bot Kit 

Step 7 — Prepare the wheel encoder magnets 

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H«n S uanir; ll*g jijh* i. 

AlUdT. II 

oriels but not 



• The robot has an 8-pole (4x north pole & 4x south pole), neodymium magnet (part #22) that 
is used to measure the distance each wheel travels. This magnet is held onto the wheel 
using a small ring of double sided tape (part #23). 

• The 8-pole magnets are only 1mm thick and very brittle. They can break easily if 
dropped or stressed. Handle with care. 

• Start by peeling away the small disc of protective layer at the center of the ring. It is much 
easier to do this first. 

• Now peel away the protective film on one side of the double sided tape and carefully align 
it with the magnet. 

• With the magnet supporting the ring of tape you can now poke the center out with the 
supplied screwdriver. 

• Repeat these steps for the second magnet. 

© Make Projects 

Page 6 of 18 

Building a Doodle Bot Kit 

Step 8 — Mount your encoder magnets on the motors 



Omm 10mm 20mm 30mm 


1 inch 


• The magnets are now ready to be mounted on the round servo horns (part #7). Pay careful 
attention to which side they mount on (see the photo). 

• Peel away the final protective layer and carefully align the magnets on the round servo 

• Now use a 2x5mm self tapping screw (part #15) to lock the servo horn in place on the 
motor output shaft. 

• Repeat these steps for the other motor. 

© Make Projects 

Page 7 of 18 

Building a Doodle Bot Kit 

Step 9 — Preparing the mounting holes for the wheels 





Omm 10mn> 20mm 3Qmn 


1 inch 

• The wheels are held on with four small 2x5mm flange head screws (part #12). These 
screws will only dig 1mm into the servo horn so as not to hit the magnet. To make sure 
they hold securely we can prethread the holes. 

• Pay carefull attention to which holes are used to ensure the holes in the wheel align 
with the holes in the servo horn. 

• First gently insert the remaining 2x5mm self tapping screw (part #15) into the holes to 
enlarge the holes. Do not go too far otherwise you may hit the magnet. 

• Now repeat the process with the 2x5mm flange head screws that will be used to hold the 
wheel on. Be careful not to push the magnet off the back of the servo horn. 


Step 10 — Mount the wheels 


• Make sure your holes align 
well before attempting to 
mount the wheel. Be careful not to 
strip the threads as there is only 

1 mm of thread. 

• You can now mount your wheels 
onto the motors using four 2x5mm 
flanged head screws (part #12). 

© Make Projects 

Page 8 of 18 

Building a Doodle Bot Kit 

Step 11 — Align and fit the servo arm 

Rotate servo fully 

anti-clockwise and 

fit servo horn 

as shown. 


• Before we can fit the servo arm 
(part #8) we must make sure it is 
properly aligned otherwise it will 
not go to the position the program 
expects it to. 

• Push the arm onto the servo output 
shaft and gently rotate 
anticlockwise until the servo will 
turn no more. 

• With the servo rotated fully 
anticlockwise we can now fit the 
servo arm in the position shown 
using the remaining 2x5mm self 
tapping screw (part #15). 

Step 12 — Mount the front roller 

• The front wheel (part #19) is just a simple roller made from a brass locking collar. A small 
brass spacer (part #24) is inserted into the collar to reduce the size of the hole. 
Sometimes the tin plating on the brass parts may cause the tube to be a tight fit in the 
collar. If so, you may need to gently press the spacer in with the screwdriver 

• This roller is fitted to the servo arm using a 2.3x1 Omm self tapping flange head screw (part 
#13). Pay careful attention to which side of the arm the roller is mounted on. Do not tighten 
the screw too far. The roller should spin freely. 

© Make Projects 

Page 9 of 18 

Building a Doodle Bot Kit 

Step 13 — Mount the battery holder 

• The robot is powered by 4x AAA alkaline or NiMh batteries. If you want to use NiMh 
batteries then you will need to modify the sample code so that the value of "lowbat" is 
approximately 470. This is explained in more detail in the manual. 

• The battery holder (part #18) is held in place with a re-usable cable tie (part #20). Thread 
the cable tie through the holes in the base plate as shown with the head at the back of the 

• Insert your battery holder (you may want to install your batteries first) and tighten the 
cable tie gently so that the battery holder cannot fall out. 

• When you need to replace the batteries, simply press down on the small lever on the cable 
tie head to release the catch and loosen the cable tie so that the battery holder can slide 
out. Install fresh batteries and re-tighten the cable tie. 

© Make Projects 

Page 10 of 18 

Building a Doodle Bot Kit 

Step 14 — Fit the controller mounting spacers 

■' 'mddle. 

• The robot control PCB (Printed Circuit Board - part #17) is mounted above the battery 
holder using 4x 30mm brass spacers (part #10). The spacers are mounted on the base 
plate using four M3x6mm machine screws (part #16) as shown in the photos. 

• Do not over tighten the screws! The base can crack if excessive force is used to tighten 
the screws. You only need to tighten the screws firmly so that friction prevents them from 
coming loose. 

• While the robot is upside down, now is a good time to feed your motor and servo cables 
through the hole at the front if you have not done so already. There is a spare hole at the 
back in case you wish to add other sensors in the future. 

© Make Projects 

Page 11 of 18 

Building a Doodle Bot Kit 

Step 15 — Mount the controller and install the rubber pen grip 

• Use the last four M3x6mm machine 
screws to mount the controller on 
the brass spacers with the USB 
(Universal Serial Bus) socket at 
the rear of the robot. 

• Press the rubber pen grip into the 
hole at the front of the base plate. 
Although the rubber grip was 
originally designed for thick 
whiteboard markers and permanent 
marker pens it can also be used for 
jumbo chalk and crayons. 

• Try inserting two or three small 
crayons or chalk sticks into the 
rubber grip for a rainbow effect. If 
you have a whiteboard marker or 
pen that is a little bit too small for 
the grip then wrap some layers of 
tape around the pen to make it 

© Make Projects 

Page 12 of 18 

Building a Doodle Bot Kit 

Step 16 — A quick tour of the Mini Driver PCB 

+V select 





D13 > > 

LED° - 

> > > > Reset 

• The Mini Driver is a low-cost robot 
controller that is ideal for 
beginners. The controller is 
compatible with an Arduino NG with 
ATmega8 and is easily 
programmed using the free Arduino 

• Unlike standard Arduino boards, 
the Mini Driver is specifically 
designed for small robots and has 
a dual motor controller built in that 
can drive 2x D.C. motors (2 amps 
each) or 1 stepper motor. 

• The digital pins are terminated in a 
3-pin male header that allows up to 
8 miniature servos to plug directly 
into the PCB and be powered 
directly from the battery. 

• Power and ground pins are also 
included with the analog inputs to 
provide power for sensors. 

• Reverse-polarity protection is built 
into the board so that accidentally 
swapping the power wires will not 
damage the board. Input voltage is 
5.5V to 10V. 

© Make Projects 

Page 13 of 18 

Building a Doodle Bot Kit 

Step 17 — Wiring up the robot 

• Doodle Bot has 2 digital sensors and one small servo that will not be under heavy load so 
we need to set V+ to 5V to prevent damage to the digital inputs. 

• Next we need to connect the motors. You can see on the control board that the motor 
outputs are labeled "ML" and "MR" for motor left and motor right. In the case of Doodle 
Bot, the "ML" output is on the right side and the "MR" output is on the left side. This is so 
that the USB socket is to the back of the robot. 

• Connect the right motor to the "MR" output and connect the left motor to the "ML" output. 
Pay careful attention to the colour of the wires. When the robot runs the sample code the 
first move it should make is to travel forward a short distance, then back up and turn anti- 

• If either motor runs backward at the beginning of the sample code then that motor needs to 
have its wires swapped over. Once the robot has gone forward and then reversed a bit, If 
the robot first turns clockwise then you need to swap left and right motors. 

• Make sure the power switch is in the off position and connect the battery holder as shown. 
The controller has reverse-polarity protection so if you accidentally connect these wires 
the wrong way the robot will not be damaged, it just won't turn on. 

© Make Projects 

Page 14 of 18 

Building a Doodle Bot Kit 

Step 18 — Wiring up the robot (continued) 

• Now connect your wheel encoder 
sensors and the servo. Note that 
the black/brown wire always goes 
to the outside of the PCB. The 
white or yellow wire is always 
closest to the processor. 

• Make sure your right wheel sensor 
connects to D2 and your left 
sensor connects to D3; otherwise 
the robot will end up running around 
in circles with one motor stopped 
and the other motor running 
continuously. The servo connects 

© Make Projects 

Page 15 of 18 

Building a Doodle Bot Kit 

Step 19 — Programming 

© Make Projects Page 16 of 18 

Building a Doodle Bot Kit 

• The manual contains detailed 
instructions for uploading the 
demonstration code into the robot. 
However, printed links to the 
software are difficult to click a 
mouse on and a pain to type. 

• To begin with you will need the 
Arduino IDE to suit your operating 
system (Windows, Mac OS X, 
Linux 32 bit or 64 bit). You can 
download the Arduino IDE for free 
from here . 

• Do not download the latest version 
as the code won't compile correctly 
and even if it did, the new versions 
compiles into a larger file that may 
not fit the limited space of the 

• The sample code was written in 
version 0022 of the IDE. You may 
find it compiles slightly smaller in 
version 0018 if you're running low 
on memory. 

• You may also need to download 
USB drivers for the CP2102 
interface. You can download the 
latest drivers for your operating 
system here . 

• Once you have the Arduino IDE 
running on your system you can 
download the sample code from 
here . You can then make the robot 
print any message you want 
following the instructions in the 

© Make Projects 

Page 17 of 18 

Building a Doodle Bot Kit 

Step 20 — What's next? 

• The Doodle Bot is not limited to just pushing a pen around all day. It is a perfect platform 
for any small robot. Add your own sensors, a small gripper, write new code for it. 

• If you need more memory then the Mini Driver can be replaced with a Micro Magician 
which includes more memory, a 3-axis accelerometer and an IR receiver. 

• Join a website such as Let's Make Robots and you can learn from and share with a 
community of fellow robot builders. 

Once you have assembled your robot, all software and sample code can be downloaded for free 
from the internet. By joining a website like Let's Make Robots you can then get help and ideas 
from fellow robot builders. 

This document was last generated on 2012-10-31 10:21:41 AM. 

© Make Projects 

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